The information I found on the interwebs left tantalizing clues, but one piece of vital information was missing. For those landing here, I'll cut to the chase:
WebAppContext webapp = new WebAppContext();
webapp.setServer(server);
webapp.setContextPath("/");
webapp.setWar("src/main/webapp");
server.setHandler(webapp);
ServerContainer wscontainer = WebSocketServerContainerInitializer.
configureContext(webapp);
wscontainer.addEndpoint(
new org.apache.wicket.protocol.ws.javax.WicketServerEndpointConfig() );
Adding the endpoint was the missing piece of the puzzle.